Portable apparatus is more and more popular, and therefore capacitor charger it uses receives more attentions than ever. Furthermore, battery is typically used for the capacitor charger, since it is the portable apparatus to employ the capacitor charger. Unfortunately, there are disadvantages to a battery serving as a power source. FIG. 1 is an illustrative diagram of a battery 102 providing a voltage Vbat and a current I to a load 104. Internally, the battery 102 includes a equivalent resistor RS and a voltage source VB, and the voltage Vbat it provides equals to the source voltage VB subtracting the voltage drop across the internal resistor RS asVbat=VB−I×RS.  [EQ-1]
FIG. 2 shows an I-V curve of the battery 102 for the voltage Vbat and the current I it supplies, in which the vertical axis represents the supplied voltage Vbat, and the horizontal axis represents the loading current I. From the equation EQ-1, the voltage Vbat varies with the current I, as shown by the I-V curve in FIG. 2, the more the current I is drawn by the load 104, the lower the voltage Vbat is provided by the battery 102. When the voltage Vbat becomes lower, the load 104 intends to draw more current I from the battery 102, and it will have the voltage Vbat to be further lower, thereby lowering the power efficiency and shortening the lifetime of the battery 102. When a battery is used to provide the power for a capacitor charger, the battery cannot provide satisfied efficiency and lifetime.
Therefore, it is desired a modulation apparatus and method for a capacitor charger to improve the power efficiency and prolong the lifetime of the battery the capacitor charger uses.